The present invention relates to a power source circuit and a method of controlling the power source circuit. In particular, the present invention relates to a power source circuit utilized for a wireless communication LSI (Large Scale Integrated circuit) and a method of controlling the power source circuit.
In a conventional LSI (Large Scale Integrated circuit) used for wireless communication, a power source circuit is provided for removing a fluctuation and a noise of a voltage supplied thereto, so that the power source circuit supplies an output voltage at a constant level with less noise to an internal circuit. It has been known that the power source circuit for supplying the output voltage includes a switching regulator of a step-down type formed of a switching element and an inductor capacitor, and a series regulator formed of a calculation amplifier and an output transistor of a linear operation type.
When a conventional communication device is designed to operate with a battery as a power source, it is desirable that the conventional communication device is operational with respect to a power source voltage within a wide range. The switching regulator outputs the power source voltage supplied from the power source to the inductor capacitor as necessary, so that the switching regulator converts the power source voltage to the output voltage. Accordingly, it is possible to minimize power loss. However, when the power source voltage is decreased, a conversion efficiency of the switching regulator tends to be deteriorated, or even the switching regulator is not able to perform the switching operation. Accordingly, the switching regulator tends to have a relatively narrow range of the appropriate voltage input from the power source.
On the other hand, the series regulator is capable of dealing with a wide range of the power source voltage, and further is capable of finely controlling the output transistor. Accordingly, it is possible to obtain the appropriate output voltage. However, when the power source voltage is high, it is necessary to drop the power source voltage to the output voltage, thereby increasing power loss.
Patent References 1 to 3 have disclosed a power source device, in which the switching regulator and the series regulator are connected in parallel or in series to utilize beneficial features of the switching regulator and the series regulator. Accordingly, the power source devices disclosed in Patent References 1 to 3 are capable of dealing with the power source voltage within a wide range while minimizing power loss.
Patent Reference 1: Japanese Patent Publication No. 2003-216247
Patent Reference 2: Japanese Patent Publication No. 05-236650
Patent Reference 3: Japanese Patent Publication No. 2009-177909
According to Patent Reference 1, the power source device is formed of the switching regulator and the series regulator connected in parallel. It is configured such that the switching regulator and the series regulator are switched according to a control signal.
According to Patent Reference 2, the power source device is formed of the switching regulator and the series regulator connected in series. In the power source device, it is possible to switch according to the power source voltage whether the switching regulator and the series regulator both are operated to generate the output voltage, or only the series regulator is operated to generate the output voltage.
According to Patent Reference 3, the power source device is formed of the switching regulator and the series regulator connected in series. Further, the power source device performs an operation in a stand-by mode or a normal mode. When the power source device performs the operation in the stand-by mode, the power source voltage is supplied to a voltage smoothing capacitor, so that it is possible to shorten a raising time upon returning to the normal mode.
As described above, in the power source device disclosed in Patent Reference 1, the switching regulator and the series regulator are connected in parallel, and are switched to generate the output voltage. Accordingly, the power source device tends to generate a large noise upon switching.
Further, in the power source devices disclosed in Patent Reference 2 and Patent Reference 3, the switching regulator and the series regulator are connected in series, and are separately controlled to operate and generate the output voltage. Accordingly, it is possible to minimize a large noise upon switching as is the case that the switching regulator and the series regulator are connected in parallel. However, it is difficult to provide a power source circuit for wireless communication capable of shortening a raising time while minimizing power consumption.
In general, an LSI used for wireless communication is provided with a lithium button battery as the power source thereof, and the lithium button battery generates the power source voltage between about 1.6 V and 3.6 V. In order to reduce the power consumption of the LSI used for wireless communication, it is necessary to intermittently terminate an operation of the LSI. Accordingly, it is configured such that the LSI switches an idle state and an operation state, thereby reducing the power consumption thereof. In a normal usage, the LSI tends to be in the idle state for a longer period of time. Accordingly, it is imperative to shorten the raising time of the LSI while reducing the power consumption thereof in the idle state.
To this end, for example, in the power source device disclosed in Patent Reference 3, the voltage smoothing capacitor is maintained at the power source potential even in the stand-by state. However, even when the voltage smoothing capacitor is maintained at the power source potential, the voltage smoothing capacitor still supplies electron charges up to the power source potential, or discharges electron charges to the voltage range of the series regulator during the operation, thereby consuming power. Accordingly, it is difficult to sufficiently reduce the power consumption.
Further, in the power source device disclosed in Patent Reference 3, in the stand-by state, the voltage smoothing capacitor is controlled at the potential significantly different from that thereof when the switching regulator performs a normal operation. Accordingly, when the power source device is transited from the stand-by state to the normal operation state, it is necessary to adjust the voltage accumulated in the voltage smoothing capacitor to a proper range. Accordingly, it is difficult to sufficiently shorten the raising time.
In view of the problems of the conventional power source devices described above, an object of the present invention is to provide a power source circuit and a method of controlling a power source circuit capable of shortening the raising time while minimizing the power consumption of the power source circuit.
Further objects and advantages of the invention will be apparent from the following description of the invention.